The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefore.
(1) Field of the Invention
The present invention relates generally to power connections and, more particularly, to a power plug adapter and method to maintain a secure power connection in the presence of shock and vibration.
(2) Description of the Prior Art
Commercial off the shelf (COTS) electrical and electronic equipment are becoming more prevalent in Naval shipboard applications due to the cost benefits associated therewith. COTS units are normally supplied with National Electrical Manufacturer""s Association (NEMA) 5-15P, three conductor power plugs, which in turn are inserted into commercial quality NEMA 5-15R power receptacles in convenience outlets, power strips, or uninterruptible power supplies. The mated commercial quality plugs and receptacles rely on the friction between the blades of the plug and the receptor devices in the outlet to hold the plug in the receptacle, even under conditions of vibration and shock. The friction fit in commercial quality plugs and receptacles provides an unreliable, inconsistent degree of restraint, and the fit degrades with repeated use. Thus, the COTS grade power plug/receptacle configuration is susceptible to unintentional power interruption caused by dislodging the plug from the receptacle under many shipboard conditions including inadvertent disconnection while cleaning or performing maintenance, mild to severe shock, and shipboard vibration conditions.
The COTS grade NEMA power plug/receptacle configuration is contrary to that found in previous shipboard Military Specifications and/or Ship Specifications. These specifications require power to be supplied via hard-wired methods or Military Specification connectors which positively secure the associated power plugs to the receptacles by mating threaded connections.
The inadvertent loss of power to equipment in response to shock could cause system reliability problems. Also, due to the high reliability of the existing hard wired and Military Specification connectors, in the event of an unexpected shut down of COTS equipment under normal and/or casualty conditions, and due to the typically difficult to reach NEMA 5-15 style power plug connections, the power conditions may not be initially checked before performing more invasive equipment troubleshooting, resulting in less efficient troubleshooting. U.S. Patents that describe attempts to provide solutions related to this problem include the following:
U.S. Pat. No. 3,358,265, issued Dec. 12, 1967, to P. O. Robards, discloses contact pins for a power control receptacle that are each provided with a hairpin spring in a contact barrel and a tab extending from a tab holder at one end.
U.S. Pat. No. 3,890,025, issued Jun. 17, 1975, to Gene L. Gray, discloses a standard, grounded three-conductor male electrical plug made to positively lock in place in its complementary female socket by friction pressure by means of a single tapered cam member which is connected to the plug body in such a way as to move longitudinally and to rotate within the split, scored ground connector of the male plug.
U.S. Pat. No. 4,111,509, issued Sep. 5, 1978, to John Novak, discloses a plug for an electrical receptacle outlet having an improved ground prong. The ground prong is supported in the plug body for axial shifting. The end of the prong extending through the plug body is threaded to engage a turn knob and the other end of the ground prong extending from the plug body for insertion in the receptacle is adapted to carry spring filaments which are supported to radially arch by the axial movement of the ground prong in response to the rotation of the knob and thereby secure the plug connected to the receptacle.
U.S. Pat. No. 4,544,216, issued Oct. 1, 1985, to R. W. Imhoff, discloses a three-prong plug including two active prongs and a grounding prong with an additional locking member which is recessed into the grounding prong. The grounding prong on the male portion of the plug has a V-shaped or U-shaped cross-section with the two sides of the electrical prong coming together with a ramp configuration at the outer end of the prong. An elongated locking member is mounted for longitudinal movement within the cross-sectional configuration of the grounding prong, with the outer end of the locking member engaging the ramp when the locking member reaches its extreme outer position to force the locking member transversely out of the recess within the U-shaped or V-shaped configuration of the third prong and into engagement with a portion of the mating female prong. In addition, arrangements are provided for normally biasing the locking member toward the outer end of the grounding prong; and release arrangements are secured to the male plug and in engagement with the locking member for unlocking the locking member and concurrently by moving the release member in a single direction for pulling the two plugs apart.
U.S. Pat. No. 5,194,013, issued Mar. 16, 1993, to Morris Propp, discloses a locking electrical plug which has a cooperating tool/key which when rotated in a first direction causes a ground prong extending therefrom to be mechanically expand within a mating female receptacle, thereby preventing inadvertent or accidental removal of the plug from the receptacle, and when rotated in a second direction this again permits the removal of the plug from the receptacle.
U.S. Pat. No. 5,249,976, issued Oct. 5, 1993, to R. D. Brock, discloses an electrical plug for 3-wire line cords that includes a plug body having a U-shaped grounding pin. A rise pin is disposed between opposing walls of the U-shaped grounding pin. A locking element extending through the plug body includes a threaded proximal portion and a flat distal portion, the distal portion having a ramp disposed over the rise pin and a serrate edge opposite the ramp with the distal portion disposed within the grounding pin opposing walls. A locking knob is threaded onto the proximal portion. With the plug in an outlet, the knob is rotated clockwise to draw the flat distal portion rearward causing the ramp to ride up the rise pin and to cause the serrate edge to grip the inner surfaces of the grounding socket. Rotating the knob counterclockwise releases the serrate edge to permit withdrawal of the plug from the outlet.
U.S. Pat. No. 6,171,129, issued Jan. 9, 2001, to D. A. Phillips, discloses an electrical adapter with dual, user-operable locking mechanisms for attachment to a standard electrical plug and outlet, one for securing the prongs of the adapter into a socket or wall-mounted outlet or receptacle and the other for securing a standard electrical plug thereto. The two mechanisms work independently of each other to secure the male and female sides of a conventional plug-and-socket combination together. The adapter can be used with existing appliances, hand tools, extension cords, and electrical outlets without the need for rewiring. The male and female ends of the adapter may be connected by an electrical cord to replace a conventional extension cord; alternatively, the locking mechanism can be built into replacement electrical plugs or a wall outlet having approximately the same dimensions as conventional outlets. Use eliminates the annoying problem of power interruptions to appliances, hand tools, and the like that occur when a plug is accidentally pulled loose from its socket. The invention also provides extra safety from electrocution and reduces spark hazards by locking the plug and socket together to help prevent accidental dislodging.
The above cited prior art does not provide a means for adapting commonly utilized NEMA power plugs normally found on COTS equipment to provide a highly reliable vibration and shock resistant power connection. Consequently, there remains a long felt but unsolved need for an improved means for connecting NEMA power plugs in a more consistently reliable manner. Those skilled in the art will appreciate the present invention that addresses the above and other problems.
Accordingly, it is an object of the present invention to provide an improved power plug and receptacle assembly and method.
Another object of the present invention is to provide a more reliable connection between a COTS power plug and corresponding power receptacle.
Another object is to provide an assembly and method as aforesaid which does not require modification or replacement of the numerous NEMA power plugs and NEMA receptacles found on COTS equipment.
These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims. However, it will be understood that above listed objects and advantages of the invention are intended only as an aid in understanding aspects of the invention, are not intended to limit the invention in any way, and do not form a comprehensive list of objects, features, and advantages.
In accordance with the present invention, an assembly is provided for use with a power plug and power plug receptacle wherein the power plug is secured to a power plug cable. The assembly may comprise one or more elements such as, for instance, an adapter with power prong connections wherein the power prong connections mate to the power plug receptacle and the adapter has an adapter receptacle operable for mating engagement with the power plug such that the adapter is operable to electrically connect the power plug to the power plug receptacle. Other elements may comprise a first locking mechanism for securing the adapter to the power plug receptacle and a second locking mechanism for securing the adapter to the power plug.
In a presently preferred embodiment, the first locking mechanism may further comprise an expandable element. The expandable element may be mounted within at least one of the power prong connections such that after the power prong connections are inserted into the power plug receptacle the expandable element is expanded to lock the adapter to the power plug receptacle.
In a presently preferred embodiment, the second locking mechanism may further comprise a restraining member mountable with respect to the power plug for securing the power plug with respect to the adapter. The restraining member may comprise split components to thereby mount onto the power plug cable. The split components are securable together such that the restraining member is secured around the power plug cable. The assembly may further comprise one or more straps interconnectable between the restraining member and the adapter to thereby secure the power plug to the adapter.
In operation, a method is provided that may be utilized for securing a NEMA power plug to a NEMA power plug receptacle to resist vibration and shock without modifying the NEMA power plug or the NEMA power plug receptacle. The method may comprise one or more steps such as, for instance, inserting an adapter into the NEMA power plug receptacle, securing the adapter to the NEMA power plug receptacle, inserting the NEMA power plug into the adapter, and/or securing the NEMA power plug to the adapter.
The method may further comprise expanding an expandable portion of at least one prong of the adapter after the adapter is inserted into the NEMA power plug receptacle and/or providing the expandable portion is comprised of an electrometric material. The method may further comprise utilizing a threaded member to apply tension to the expandable portion.
The method may further comprise mounting a restraining member to the cable adjacent the NEMA power plug and/or connecting one or more straps between the restraining member and the adapter. In a preferred embodiment, the method may further comprise utilizing split elements to form the restraining member to the cable and/or utilizing one or more straps to secure the split elements together around the cable.
The method may further comprise providing at least one first loop on the adapter and at least one second loop on the restraining member and/or inserting one or more flexible straps into the first loop and the second loop.
In another embodiment, the invention comprises an assembly with one or more elements such as an adapter with power prong connections wherein the power prong connections mate to the power plug receptacle and the adapter has at least one adapter receptacle operable for mating engagement with at least one power plug, and a first locking mechanism for securing the adapter to the power plug receptacle. The first locking mechanism further comprises an expandable element mounted within at least one of the power prong connections such that after the power prong connections are inserted into the power plug receptacle and the expandable element is expandable to lock the adapter to the power plug receptacle. The assembly may comprise an axially moveable tensioner such that the tensioner is moveable against the expandable element to urge the expandable element to expand radially outwardly.